Parkinson's disease is characterized neuropathologically by degeneration of dopamine neurons in the basal ganglia and neurologically by debilitating tremors, slowness of movement and balance problems. It is estimated that over one million people suffer from Parkinson's disease. Nearly all patients receive the dopamine precursor levodopa or L-Dopa, often in conjunction with the dopa-decarboxylase inhibitor, carbidopa. L-Dopa adequately controls symptoms of Parkinson's disease in the early stages of the disease. However, it tends to become less effective after a period which can vary from several months to several years in the course of the disease.
It is believed that the varying effects of L-Dopa in Parkinson's disease patients is related, at least in part, to the plasma half life of L-Dopa which tends to be very short, in the range of 1 to 3 hours, even when co-administered with carbidopa. In the early stages of the disease, this factor is mitigated by the dopamine storage capacity of the targeted striatal neurons. L-Dopa is taken up and stored by the neurons and is released over time. However, as the disease progresses, dopaminergic neurons degenerate, resulting in decreased dopamine storage capacity. Accordingly, the positive effects of L-Dopa become increasingly related to fluctuations of plasma levels of L-Dopa. In addition, patients tend to develop problems involving gastric emptying and poor intestinal uptake of L-Dopa. Patients exhibit increasingly marked swings in Parkinson's disease symptoms, ranging from a return to classic Parkinson's disease symptoms, when plasma levels fall, to the so-called dyskinesis, when plasma levels temporarily rise too high following L-Dopa administration.
As the disease progresses, conventional L-Dopa therapy involves increasingly frequent, but lower dosing schedules. Many patients, for example, receive L-Dopa every two to three hours. It is found, however, that even frequent doses of L-Dopa are inadequate in controlling Parkinson's disease symptoms. In addition, they inconvenience the patient and often result in non-compliance.
It is also found that even with as many as six to ten L-Dopa doses a day, plasma L-Dopa levels can still fall dangerously low, and the patient can experience very severe Parkinson's disease symptoms. When this happens, additional L-Dopa is administered as intervention therapy to rapidly increase brain dopamine activity. However, orally administered therapy is associated with an onset period of about 30 to 45 minutes during which the patient suffers unnecessarily. In addition, the combined effects of the intervention therapy, with the regularly scheduled dose can lead to overdosing, which can require hospitalization. For example, subcutaneously administered dopamine receptor agonist (apomorphine), often requiring a peripherally acting dopamine antagonist, for example, domperidone, to control dopamine-induced nausea, is inconvenient and invasive.
Other medical indications involving the central nervous system (CNS) require rapid delivery of a medicament such as but not limited to epilepsy, panic attacks and migraines. For example, about 2 million people in the USA suffer from some form of epilepsy, with the majority receiving at least one of several different anti-seizure medications. The incidence of status epilepticus (the more serious form of epilepsy) is approximately 250,000. A significant number of patients also suffer from so-called “cluster seizures”, wherein an initial seizure forewarns that a series of additional seizures will occur within a relatively short time frame. By some reports, 75% of all patients continue to experience seizures despite taking medication chronically. Poor compliance with the prescribed medications is believed to be a significant (albeit not sole) contributing factor. The importance of controlling or minimizing the frequency and intensity of seizures lies in the fact that incidence of seizures has been correlated with neuronal deficits and is believed to cause loss of neurons in the brain.
Despite chronic treatment, as many as 75% of all patients continue to exhibit periodic seizures. The uncontrolled seizures occur in many forms. In the case of “cluster seizures,” one seizure serves notice that a cascade has begun which will lead to a series of seizures before the total episode passes. In certain patients, prior to the onset of a severe seizure, some subjective feeling or sign is detected by the patient (defined as an aura). In both instances, an opportunity exists for these patients to significantly reduce the liability of the seizure through “self medication”. While many patients are instructed to do so, the drugs currently available to permit effective self medication are limited.
Panic attacks purportedly affect at least about 2.5 million people in this country alone. The disorder is characterized by acute episodes of anxiety, leading to difficult breathing, dizziness, heart palpitations and fear of losing control. The disorder is believed to involve a problem with the sympathetic nervous system (involving an exaggerated arousal response, leading to overstimulation of adrenaline release and/or adrenergic neurons). Current pharmacotherapy combines selective serotonin re-uptake inhibitors (SSRIs), or other antidepressant medications, with the concomitant use of benzodiazapines.
A limitation of the pharmacotherapies in current use is the delay in the onset of efficacy at the beginning of treatment. Like treatments for depression, the onset of action of the SSRIs requires weeks rather than days. The resulting requirement for continuous prophylactic treatment can, in turn, lead to significant compliance problems rendering the treatment less effective. Therefore, there is a need for rapid onset therapy at the beginning of treatment to manage the anticipation of the panic attacks, as well as a treatment for aborting any attacks as soon as possible after their occurrence.
A pure vasogenic etiology/pathogenesis for migraine was first proposed in the 1930s; by the 1980s, this was replaced by a neurogenic etiology/pathogenesis, which temporarily won favor among migraine investigators. However, it is now generally recognized that both vasogenic and neurogenic components are involved, interacting as a positive feedback system, with each continuously triggering the other. The major neurotransmitters implicated include serotonin (the site of action of the triptans), substance P (traditionally associated with mediating pain), histamine (traditionally associated with inflammation) and dopamine. The major pathology associated with migraine attacks include an inflammation of the dura, an increase in diameter of meningeal vessels and supersensitivity of the trigeminal cranial nerve, including the branches that enervate the meningeal vessels. The triptans are believed to be effective because they affect both the neural and vascular components of the migraine pathogenic cascade. Migraines include Classic and Common Migraines, Cluster Headaches and Tension Headaches.
Initial studies with sumatriptain showed that, when administered intravenously (IV), a 90% efficacy rate was achieved. However, the efficiency rate is only approximately 60% with the oral form (versus 30% for placebo). The nasal form has proven to be highly variable, requiring training and skill on the part of the patient, which some of the patients do not seem to master. The treatment also induces a bad taste in the mouth which many patients find highly objectionable. There currently exists no clear evidence that any of the recent, more selective 5HT1 receptor agonists are any more efficacious than sumatriptan (which stimulates multiple receptor subtypes; e.g., 1B, 1D, and 1F).
In addition to not providing adequate efficacy, current dosing of triptans have at least two other deficiencies: (1) vasoconstriction of chest and heart muscles, which produces chest tightness and pain in some subjects; this effect also presents an unacceptable risk to hypertensive and other CV patients, for whom the triptans are contraindicated, and (2) the duration of action of current formulations is limited, causing a return of headache in many patients about 4 hours after initial treatment.
Rapid onset of a hypnotic would also be quite desirable and particularly useful in sleep restoration therapy, as middle of night awakening and difficulty in falling asleep again, once awakened, is common in middle aged and aging adults.
Other indications related to the CNS, such as, for example, mania, bipolar disorders, schizophrenia, appetite suppression, motion sickness, nausea and others, as known in the art, also require rapid delivery of a medicament to its site of action.
Therefore, a need exists for methods of delivery of medicaments which are at least as effective as conventional therapies yet minimize or eliminate the above-mentioned problems.